I've been putting a bird suet cage on my apartment windowsill for about the last year. I keep it from falling off with a piece of twine, which I shut inside the window so the suet can't fall down. Squirrels discovered my suet cage and bird food, and managed to knock it off the windowsill so that it dangled vertically, by the twine. That was serendipitious. There are some birds around here, like Downy Woodpeckers and White-Breasted Nuthatches, that will only feed at the suet cage if they can cling in a vertical position. Now I've gone from occasionally seeing these birds in and around the feeder, to seeing them every day, and the accident has become a permanent fixture.
It only matters because, as the leaves fall off the trees and the rest of Chicago's natural world takes on a more empty feel, the birds become one of the more obvious naturalistic objects of interest. The window that I sit next to every day just got more interesting for the winter.
Richard N. Conner. "Orientation of Entrances to Woodpecker Nest Cavities." The Auk, Apr., 1975, Vol. 92, No. 2 (Apr., 1975), pp. 371-374.